We will evaluate the effects of a school-based aerobic exercise intervention on blood pressure (BP) and insulin resistance (IR) in black female adolescents at increased risk for essential hypertension (EH). Changes in cardiovascular reactivity, peripheral vascular resistance (PVR), and self-perception also will be examined. Students entering high school (Grade 9) will be screened on BP, anthropometrics, and aerobic fitness; those with repeated BP values in the top quartile relative to peers will be assessed on CV reactivity and fasting insulin, then recruited into an experiment to be conducted as part of the required physical education (PE) curriculum. By screening 900 students in 3 successive 9th grade cohorts, a total sample of 135 subjects will be selected and evaluated over a 4-year period. Eligible subjects (N = 135) entering 10th grade will be randomized to a 1st semester aerobic exercise PE class or to no PE. In 2nd semester, these assignments will be reversed, permitting cross-over comparison of exercise effects. Analyses will test study hypotheses that aerobic exercise will lower BP, IR, and PVR; exercise-induced BP changes will be related to decreased IR independent of weight/adiposity changes; and reduced BP reactivity and beneficial psychological changes will be associated with exercise-induced lowering of IR. Predictors of BP, PVR, and insulin changes will be identified. The high school in which these studies will be performed is the site of the Principal Investigator's current investigation entitled, "Adolescent BP Variation and Left Ventricular Mass" (R01-HL-36298); nearly all of the proposed measurement protocols have been used extensively in this project and setting.